Zig creator on Bun's Rust rewrite: 'We breathed a sigh of relief'

Key Takeaways

• Andrew Kelley claims Bun's codebase was 'hacks on top of hacks' and represented 'how not to write Zig code'
• The Zig Software Foundation stopped receiving $60,000/year in donations when Anthropic acquired Bun
• Kelley criticizes VC-backed open source for prioritizing speed over code quality and maintainer sustainability

Andrew Kelley, creator of the Zig programming language, has published a scathing account of his relationship with Bun and its founder Jarred Sumner. The post arrives weeks after Bun announced it would rewrite major components from Zig to Rust following its acquisition by Anthropic. Kelley's verdict: the Zig Software Foundation is better off without Bun as its flagship project.

The blog post reads less like technical commentary and more like a breakup letter. Kelley accuses Sumner of poor management, reckless engineering practices, and building what he calls 'slop well before he had access to LLMs.' The Zig team, he writes, had come to view Bun as a 'net liability' despite its role in popularizing the language.

What happened between Zig and Bun?

Kelley traces the relationship back five years, when Sumner joined the Zig community. He describes Sumner as having 'beginner energy,' moving fast and learning by doing. That approach worked for a solo developer. It became a problem, Kelley argues, when Sumner took venture capital and started managing a team.

Sumner raised $7 million from investors including Kleiner Perkins in 2022. He also set up monthly donations to the Zig Software Foundation totaling $60,000 per year. Kelley acknowledges this was generous. But the money came with baggage.

“Once Bun became a VC-backed startup, he started racing towards the finish line. Now, instead of working on a free and open source project, learning and growing with the community, Jarred was running a business.”

— Andrew Kelley, Creator of Zig

The Zig team began auditing Bun's codebase as part of their standard practice of checking in on major projects using the language. What they found alarmed them: 'Hacks on top of hacks. Abuse of assertions. Most of all, recklessly speeding past feature after feature with very little time taken for reflection and elimination of bugs and technical debt.'

Why does code quality matter for Zig's reputation?

Zig positions itself as a safer alternative to C, with explicit memory management and compile-time guarantees. Critics constantly push back on this claim, pointing to memory safety concerns. Having the most visible Zig project exemplify sloppy practices undermined the language's pitch.

Kelley frames this as an existential PR problem: 'You can imagine how we might want to put some social distance between ourselves and a project whose irresponsible software engineering practices invite the exact kind of criticism that people are eager to level.'

The Zig team tried to intervene. They made 'futile attempts to guide them towards better programming practices.' A few engineers at Oven, Bun's parent company, pushed back internally. But the pressure to ship won out.

What does Kelley say about Oven's workplace culture?

Kelley's harshest criticism targets Sumner's management. He claims to have spoken with candidates who interviewed at Oven and employees who worked there. The consistent message: 'Poor communication, unrealistic expectations, low empathy, no experience. Just a total shit show, from an employment perspective.'

This reputation allegedly kept Zig's best developers away. Despite strong interest in paid Zig work, 'most of the talent pool steered clear of Oven and Bun.'

Kelley attributes part of this to Sumner's background. Having 'graduated from the Thiel Fellowship school of thought rather than university,' Sumner was 'essentially groomed from a young age into uncritically embracing the Silicon Valley mindset.' The Thiel Fellowship, funded by Peter Thiel, pays students to drop out of college and start companies.

How did the Anthropic acquisition change things?

When Anthropic acquired Bun earlier this year, the Zig Software Foundation had already written off the relationship. The $60,000 annual donation stopped. A scheduled monthly meeting went unanswered. Kelley says none of this surprised them.

'When the Anthropic acquisition finally happened, we at ZSF breathed a sigh of relief,' Kelley writes. The foundation had prepared its finances for the donation to end.

The Rust rewrite confirms the split. Bun's decision to move away from Zig removes the uncomfortable association Kelley describes. It also raises questions about what Anthropic sees in Bun's infrastructure that makes it worth acquiring and rebuilding.

What does this mean for the Zig ecosystem?

Losing Bun removes Zig's most visible consumer-facing project. JavaScript remains the world's most popular programming language, and Bun reached version 1.0 in September 2023 with real adoption. That exposure helped attract developers to Zig.

But Kelley seems unbothered. The post suggests he prefers a smaller community of careful engineers to a larger one attracted by flashy but flawed showcase projects. Whether that strategy sustains Zig's growth remains to be seen.

Frequently Asked Questions

Why is Bun rewriting from Zig to Rust?

Bun has not fully explained the technical rationale, but the rewrite follows Anthropic's acquisition. Andrew Kelley suggests the Bun codebase had accumulated significant technical debt that may have made maintenance difficult regardless of language choice.

Is Zig or Rust better for systems programming?

Both languages target similar use cases. Zig emphasizes simplicity and C interoperability. Rust emphasizes memory safety through its borrow checker. The choice depends on team expertise and project requirements.

How much was Bun donating to the Zig Software Foundation?

Bun's parent company Oven donated $60,000 per year to the Zig Software Foundation. These donations stopped after Anthropic acquired Bun.

What is the Thiel Fellowship?

The Thiel Fellowship, funded by billionaire Peter Thiel, pays students under 23 up to $100,000 to drop out of college and pursue startups or research. Bun creator Jarred Sumner is a Thiel Fellow.

Is Bun still open source after the Anthropic acquisition?

Bun remains open source under the MIT license as of this writing. Anthropic has not announced changes to its licensing.

Source: Hacker News: Best